in previous versions of artweaver I could open png images as multiple layers, or even drag and drop them. for some reason this version is not letting me do this. Is this a setting? Or do I need a plugin?

Older Artweaver versions had no support for transparent layers as background (e.g. first layer) and therefore PNG documents with transparency where loaded into a second layer over the always existing background layer.

This has changed and now PNG documents with transparency are only loaded into one single layer with transparency. If you want a background layer back you can create a new layer, move it below the first layer and fill it with any color.